A heatmap of keypoints encodes the center of a 2D human body in the image, where the activation value at each position indicates the degree to which the keypoint lies in position. The position of each joint is represented as a gaussian distribution in the heatmap, and we use PAFs to link the identity-agnostic joints from the keypoint heatmaps after non-maximum suppression following [1]}.
Then, we can get the 2D joints location \((u_k^{hm}, v^{hm}_k)^T\)  at image pixel coordinate from heatmap scheme.
